This invention relates generally to multi-cavity injection molding apparatus for three layer molding and more particularly to such apparatus wherein an elongated pin extending through a central melt channel in each heated nozzle has a central melt bore extending rearwardly from its front end.
Multi-cavity injection molding apparatus for making three layer protective containers for food or preforms or parisons for beverage bottles are known. One layer of a barrier material such as ethylene vinyl alcohol copolymer (EVOH) or nylon is molded between two layers of a polyethylene terephthalate (PET) type material. In some multi-cavity apparatus the two different melts are distributed through a single melt distribution manifold having two melt passages, but preferably for materials such as these having different injection temperatures of about 400.degree. F. and 565.degree. F. respectively, the two melts are distributed through two different melt distribution manifolds. In some cases, the two melts are injected sequentially, while in other cases both coinjection and sequential injection are utilized. The two melts are both injected through a heated nozzle having a central melt channel and an annular melt channel extending around the central melt channel to a gate leading to the cavity.
As seen in U.S. Pat. No. 4,717,324 to Schad et al. which issued Jan. 5, 1988, valve gated apparatus has been used for three layer molding. However, that apparatus has the disadvantage that it does not disclose sprue gating apparatus and also that the valve gated apparatus does not allow simultaneous or coinjection of the two melts.